"Look at the DV percentage. The percentage of Daily Value is based on chemically pure vitamin fractions. If the nutrient on the label is listed at 100% or more, you've likely got a synthetic product on your hands. Remember, nature is low dose but highly potent.
Beware of singular vitamins. Mother Nature works in tandem. Her nutrients are never found alone. If you’re taking a supplement all by itself, such as vitamin E or D, it’s guaranteed to be synthetic.
Don’t buy the hype. The supplement industry is an industry just like anything else. Major supplement manufacturers often sponsor studies and/or donate money to research programs at universities likely having some influence on both the study design and the results and conclusions reached." (Ex. Fish oil supplements became very popular within recent years but without specific heart conditions fish oil supplements can actually create health problems in healthy individuals. While they can be very helpful for people in a specific situation they are not a good choice for the average person trying to take care of their heart health.)
and one more important bit of my own.
Research your company. Harmful levels of heavy metals or bacteria have been found in bottles of well intention supplement takers pill bottles on several occasions even within the past decade. If you are going to take supplements do research on the manufacturer to ensure they are providing only the best and safest products. Good places to start would include consumer reports or other resources outside the company itself.
And also ask yourself the following questions (from WebMD)
-"What health benefits does this supplement offer me?
-Is there any research supporting the use of this supplement?
-Do I need this supplement for my health, either to treat a medical condition or help prevent disease?
-What is the recommended dose for this supplement?
-When and for how long do I need to take this supplement?
-Which is most appropriate and effective for me -- a pill, powder, or liquid?
-Which form of the vitamin (vitamin D2 or D3, for instance) is the best?
-Does this supplement or vitamin have any known side effects?
-What are the best brands of this supplement in terms of quality, safety, and researched effectiveness?
-Does this supplement interact with any medications or foods?
-Will I need to stop taking this supplement or vitamin if I have to undergo surgery?"